MFC r271597:

Pull in r217410 from upstream llvm trunk (by Bob Wilson):

  Set trunc store action to Expand for all X86 targets.

  When compiling without SSE2, isTruncStoreLegal(F64, F32) would return
  Legal, whereas with SSE2 it would return Expand. And since the Target
  doesn't seem to actually handle a truncstore for double -> float, it
  would just output a store of a full double in the space for a float
  hence overwriting other bits on the stack.

  Patch by Luqman Aden!

This should fix clang -O0 on i386 assigning garbage to floats, in
certain scenarios.

PR:		187437
Submitted by:	cebd@gmail.com
Approved by:	re (marius)
Obtained from:	http://llvm.org/viewvc/llvm-project?rev=217410&view=rev